Abstract: The failure diagnosis apparatus whether or not a failure exists in a fuel-evaporation-gas purging system that a negative pressure in an intake system of an internal combustion engine is introduced into an accumulator and pressure accumulation is performed in a time period from a time when a driver turns off an ignition key to a time when the internal combustion engine stops its rotation, that the accumulated negative pressure is introduced into a fuel-evaporation-gas path before the internal combustion engine stops the rotation or after the internal combustion engine has stopped the rotation, and that in a time from a time when after the internal combustion engine has stopped the rotation, the driver again turns on the ignition key to a time when the internal combustion engine starts, it is determined whether or not a pressure change in the fuel-evaporation-gas path exists.